U.S. Pat. No. 4,589,905 discloses the use of 1alkyl-5-cyano-1H-pyrazole-4-carboxylic acid esters as intermediates to carboxamide herbicides and algicides. The intermediates are prepared by a multi-step process which includes reacting an alkylhydrazine with an alkyl .alpha.-acetyl-.alpha.-(dimethylaminomethylene)acetate to produce a 1-alkyl-5-methyl-1H-pyrazole-4-carboxylic acid ester, followed by conversion of the 5-methyl group to a 5-cyano group.
This invention concerns synthesis of these intermediates by direct alkylation of pyrazoles. While pyrazoles can be alkylated by a number of methods, most methods alkylate at both ring nitrogen atoms, thereby producing a mixture of alkylated products that is often difficult to separate. An object of the present invention is to provide a process for alkylating certain pyrazoles predominantly at only one of the ring nitrogen atoms, resulting in essentially pure alkylated product. A second object of the present invention is to provide new compounds; namely, 3(5)-cyano-1H-pyrazole-4-carboxylic acid esters.